Method and apparatus for controlling transmission power in a potentially transmission gated or capped communication system

ABSTRACT

A power control system for controlling the transmission power in a system wherein the transmission power may be gated or capped. The receiver employs a combination of closed loop and outer loop power control. The outer loop is frozen upon detection by the receiver that the signal has been capped or gated.

CROSS REFERENCE

[0001] This application claims priority from co-pending U.S. applicationSer. No. 09/239,454, filed Jan. 28, 1999, entitled “Method and Apparatusfor Controlling Transmission Power in a Potentially Transmission Gatedor Capped Communication System” and currently assigned to the assigneeof the present application.

BACKGROUND OF THE INVENTION

[0002] I. Field of the Invention

[0003] The present invention relates to communications. Moreparticularly, the present invention relates to a novel and improvedmethod and apparatus for controlling transmission power in a wirelesscommunication system.

[0004] II. Description of the Related Art

[0005] The use of code division multiple access (CDMA) modulationtechniques is one of several techniques for facilitating communicationsin which a large number of system users are present. Other multipleaccess communication system techniques, such as time division multipleaccess (TDMA) and frequency division multiple access (FDMA) are known inthe art. However, the spread spectrum modulation technique of CDMA hassignificant advantages over these modulation techniques for multipleaccess communication systems. The use of CDMA techniques in a multipleaccess communication system is disclosed in U.S. Pat. No. 4,901,307,entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USINGSATELLITE OR TERRESTRIAL REPEATERS”, assigned to the assignee of thepresent invention, of which the disclosure thereof is incorporated byreference herein. The use of CDMA techniques in a multiple accesscommunication system is further disclosed in U.S. Pat. No. 5,103,459,entitled “SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMACELLULAR TELEPHONE SYSTEM”, assigned to the assignee of the presentinvention, of which the disclosure thereof is incorporated by referenceherein.

[0006] CDMA by its inherent nature of being a wideband signal offers aform of frequency diversity by spreading the signal energy over a widebandwidth. Therefore, frequency selective fading affects only a smallpart of the CDMA signal bandwidth. Space or path diversity is obtainedby providing multiple signal paths through simultaneous links from amobile user through two or more cell-sites. Furthermore, path diversitymay be obtained by exploiting the multipath environment through spreadspectrum processing by allowing a signal arriving with differentpropagation delays to be received and processed separately. Examples ofpath diversity are illustrated in U.S. Pat. No. 5,101,501 entitled“METHOD AND SYSTEM FOR PROVIDING A SOFT HANDOFF IN COMMUNICATIONS IN ACDMA CELLULAR TELEPHONE SYSTEM”, and U.S. Pat. No. 5,109,390 entitled“DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM”, both assignedto the assignee of the present invention and incorporated by referenceherein.

[0007] A method for transmission of speech in digital communicationsystems that offers particular advantages in increasing capacity whilemaintaining high quality of perceived speech is by the use of variablerate speech encoding. The method and apparatus of a particularly usefulvariable rate speech encoder is described in detail in U.S. Pat. No.5,414,796, entitled “VARIABLE RATE VOCODER”, assigned to the assignee ofthe present invention and incorporated by reference herein.

[0008] The use of a variable rate speech encoder provides for dataframes of maximum speech data capacity when said speech encoding isproviding speech data at a maximum rate. When a variable rate speechcoder is providing speech data at a less that maximum rate, there isexcess capacity in the transmission frames. A method for transmittingadditional data in transmission frames of a fixed predetermined size,wherein the source of the data for the data frames is providing the dataat a variable rate is described in detail in U.S. Pat. No. 5,504,773,entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FORTRANSMISSION”, assigned to the assignee of the present invention, ofwhich the disclosure thereof is incorporated by reference herein. In theabove mentioned patent application a method and apparatus is disclosedfor combining data of differing types from different sources in a dataframe for transmission.

[0009] In frames containing less data than a predetermined capacity,power consumption may be lessened by transmission gating a transmissionamplifier such that only parts of the frame containing data aretransmitted. Furthermore, message collisions in a communication systemmay be reduced if the data is placed into frames in accordance with apredetermined pseudorandom process. A method and apparatus for gatingthe transmission and for positioning the data in the frames is disclosedin U.S. Pat. No. 5,659,569, entitled “DATA BURST RANDOMIZER”, assignedto the assignee of the present invention, of which the disclosurethereof is incorporated by reference herein.

[0010] A useful method of power control of a mobile in a communicationsystem is to monitor the power of the received signal from the mobilestation at a base station. The base station in response to the monitoredpower level transmits power control bits to the mobile station atregular intervals. A method and apparatus for controlling transmissionpower in this fashion is disclosed in U.S. Pat. No. 5,056,109, entitled“METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMACELLULAR MOBILE TELEPHONE SYSTEM”, assigned to the assignee of thepresent invention, of which the disclosure thereof is incorporated byreference herein.

[0011] In a communication system that provides data using a QPSKmodulation format, very useful information can be obtained by taking thecross product of the I and Q components of the QPSK signal. By knowingthe relative phases of the two components, one can determine roughly thevelocity of the mobile station in relation to the base station. Adescription of a circuit for determining the cross product of the I andQ components in a QPSK modulation communication system is disclosed inU.S. Pat. No. 5,506,865, entitled “PILOT CARRIER DOT PRODUCT CIRCUIT”,assigned to the assignee of the present invention, the disclosure ofwhich is incorporated by reference herein.

[0012] There has been an increasing demand for wireless communicationssystems to be able to transmit digital information at high rates. Onemethod for sending high rate digital data from a remote station to acentral base station is to allow the remote station to send the datausing spread spectrum techniques of CDMA. One method that is proposed isto allow the remote station to transmit its information using a smallset of orthogonal channels, this method is described in detail incopending U.S. Pat. No. 08/886,604, entitled “HIGH DATA RATE CDMAWIRELESS COMMUNICATION SYSTEM”, assigned to the assignee of the presentinvention and incorporated by reference herein.

SUMMARY OF THE INVENTION

[0013] The present invention is a novel and improved power controlsystem for use in a communication system in which the transmissionenergy may be gated or capped or closed loop power control commandsotherwise ignored without the knowledge of the transmitter of thosepower control commands. The present invention is illustrated in thecontext of controlling forward link transmission power. It will beunderstood by one skilled in the art that the present invention isequally applicable to controlling the reverse link transmission powerand that the invention is in no way limited to the application offorward link power control. Simply, by exchanging the references of themobile station to references of a base station and changing referencesof the base station to references to the mobile station, a reverse linkpower control system is described.

[0014] In mobile station 7, the forward link signals 3 are received anddemodulated. In addition, the mobile station determines the adequacy ofthe received signal power of forward link signals 3. In accordance withthe determined adequacy of the received signal energy of forward linksignals 3, mobile station 7 generates a series power control commands.In the exemplary embodiment, the power control commands consist of aseries of simple up/down commands to which base station 1 responds byincreasing or decreasing the transmission energy of forward link signals3. The present invention is equally applicable to the generation ofother forms of closed loop power control, such as the generation ofpower control commands that are indicative of the amount of change tothe transmission power of forward link signals 3.

[0015] In the exemplary embodiment, power control commands are generatedby comparing the received signal to interference ratio (SIR) of forwardlink signals 3 to at least one signal to interference ratio threshold.In the exemplary embodiment, a single signal to interference ratiothreshold is used in the generation of a one bit power control command.The signal to energy ratio threshold is set to provide a desiredperformance level, such as a desired frame error rate or symbol errorrate. This desired performance level may vary based upon the type ofservice being provided on forward link signal 3. When the performancelevel of the received forward link signal 3 varies from the desiredperformance level, the signal to interference ratio threshold ischanged.

[0016] If the performance level of the received signal is less than thedesired performance level, then the signal to interference ratiothreshold is increased which will result in an increase in the receivedenergy of forward link signals 3. Conversely, if the performance levelof the received signal is greater than the desired performance level,then the signal to interference ratio threshold is decreased. It mayseem counter intuitive to speak of a received signal being of too greata quality, but it should be remembered that this excess qualityrepresents unnecessary energy employed in the transmission of forwardlink signals 3, which results in degradation of service to all othermobile stations served by base station 1 and to a reduction in thenumber of mobile station capable of being served by base station 1.

[0017] The varying of the signal to interference ratio thresholds basedon measured performance metrics is referred to as outer loop powercontrol. The feedback of power control commands based on comparing themeasured signal to interference ratio to the variable threshold isreferred to as closed loop power control. The combination of closed loopand outer loop power control is contemplated in both the ETSI UTRAcandidate submission and the TIA cdma2000 candidate submission. Thecombination of closed loop power control and open loop power control isdescribed in detail in aforementioned U.S. Pat. No. 5,056,109.

[0018] Mobile station 7 generates the power control commands andtransmits them along with traffic data, pilot symbol data back to basestation 1 on reverse link signals 5. In the exemplary embodiment,reverse link signals 5 are CDMA signals. In particular, in the exemplaryembodiment, reverse link signals 5 are CDMA signals transmitted inaccordance with the description in both the ETSI UTRA candidatesubmission and the TIA cdma2000 candidate submission. The reverse linksignals for these two submissions are essentially identical for thepurposes of the present invention. It should be understood that thepresent invention is equally applicable to other forms of CDMA signalsand to other modulation schemes such as TDMA or GSM modulation schemes.

[0019] Base station 1 receives the power control commands from mobilestation 7, and in response to those commands increases or decreases thetransmission energy of forward link signals 3. However, there may betimes when base station 1 does not respond to the power control commandsfrom mobile station 7. For example, base station 1 may not increase theenergy of forward link signals 3 in response to power control commandsfrom mobile station 7, when base station 1 determines that it cannotallocate additional energy for the transmission to forward link signals3 without causing unacceptable degradation to the transmission ofsignals to other mobile stations served by base station 1.

[0020] When base station 1 does not respond to the power controlcommands from mobile station 7, it can either continue transmitting atthe present transmission energy of forward link signals 3 (referred toherein in as “capping” the energy of forward link signals 3) or it cantemporarily gate off the transmission of forward link signals 3(referred to herein in as “gating” the energy of forward link signals3). When the energy of forward link signals 3 is either capped or gated,reception of those frames or symbols transmitted at the capped or gatedenergy in error may be unreliable.

[0021] Under traditional implementations, in response to the receptionof the capped or gated frames or symbols, mobile station 7 willerroneously increase its signal to interference ratio threshold in theouter loop power control adjustment described above. This adjustmentmust be inhibited because the cause of the frame or symbols errors isnot a result of mobile station 7 sending incorrect power controlcommands but rather because base station 1 is ignoring those commandsand this is not within the control of mobile station 7. The presentinvention addresses this problem of controlling adjustment of the outerloop power control system in the presence of potentially gated or cappedsignals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The features, objects, and advantages of the present inventionwill become more apparent from the detailed description set forth belowwhen taken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

[0023]FIG. 1 is a block diagram illustrating the two basic components ofa wireless communication system the base station and the mobile station;

[0024]FIG. 2 is a block diagram of the base station of the presentinvention; and

[0025]FIG. 3 is a block diagram of the mobile station of the presentinvention.

[0026] FIGS. 4-5 are flow diagrams of power control at a mobile station.

[0027]FIG. 6 is a timing diagram of power control operation at a mobilestation.

[0028]FIG. 7 is a timing diagram of power control operation of a basestation for capped or gated signals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Outer Loop Control in a Potentially Gated or Capped TransmissionSystem

[0030] Referring to FIG. 1, a wireless communication system isillustrated in which base station 1 transmits a wireless communicationsignal 3 to mobile station 7. Transmissions from base station 1 tomobile station 7 are referred to as forward link transmissions. In theexemplary embodiment, the wireless communication signals 3 and 5 aretransmitted using a code division multiple access (CDMA) modulation. Thegeneration of CDMA signals is well known in the art and is described indetail in the aforementioned U.S. Pat. Nos. 4,901,307 and 5,103,459 andis standardized in Telecommunications Industry Association InterimStandard TIA/EIA/IS-95-A, entitled “MOBILE STATION-BASE STATIONCOMPATIBILITY STANDARD FOR DUAL-MODE WIDEBAND SPREAD SPECTRUM CELLULARSYSTEM” (hereafter the proposed IS-95 standard). The present inventionis equally applicable to all wireless communication systems employing acombined closed loop and outer loop power control system.

[0031] The Telecommunications Industry Association proposed an evolutionof the IS-95 standard that provides for high speed data transmission inits submission to the ITU entitled “THE CDMA2000 ITU-R RTT CANDIDATESUBMISSION”. Similarly, the European Telecommunications StandardsIndustry (ETSI) has proposed an alternative evolution of secondgeneration CDMA systems in its proposal to the ITU entitled “THE ETSIUMTS TERRESTRIAL ACCESS (UTRA) ITU-R RTT CANDIDATE SUBMISSION”. Thepresent invention is particularly well suited for application to highrate CDMA communication systems, because the transmission of high speeddata in a wireless communication system results more frequently in theinability to provide sufficient transmission power to reliably transmitthe data. Thus, in the exemplary embodiment, the forward link signals 3are CDMA high speed data signals as described in the cdma2000 and UTRAproposals. It will be understood by one skilled in the art that thepresent invention is also applicable to other wireless communicationsystems.

[0032] In the exemplary embodiment, forward link communications signals3 include: pilot signals to allow for coherent demodulation by mobilestation 7, primary traffic data, supplemental high speed data and powercontrol signals. It will understood by one skilled in the art that thelist of information transmitted within forward link signals 3 is not allinclusive, nor need all the information listed be present in order toapply the present invention. Moreover, it will be understood that thepresent invention is equally applicable to power control of the reverselink signals.

[0033] In mobile station 7, the forward link signals 3 are received anddemodulated. In addition, mobile station 7 determines the adequacy ofthe received signal power of forward link signals 3. In accordance withthe determined adequacy of the received signal energy of forward linksignal 3, mobile station 7 generates a series of power control commands.In the exemplary embodiment, the power control commands consist of aseries of one bit up/down commands to which base station 1 responds byincreasing or decreasing the transmission energy of forward link signals3. The present invention is equally applicable to the generation ofother forms of closed loop power control, such as the generation ofpower control commands that are indicative of the amount of change tothe transmission power of forward link signals 3.

[0034] In the exemplary embodiment, power control commands are generatedby comparing the estimated received signal to interference ratio (SIR)of forward link signals 3 to a signal to interference ratio threshold.The signal to interference ratio threshold is set so as to provide for adesired performance level, such as a desired frame error rate or symbolerror rate. This desired performance level may vary based upon the typeof service being provided on forward link signal 3. When the performancelevel of the received forward link signal 3 varies from the desiredperformance level, the signal to interference ratio threshold ischanged.

[0035] If the performance level of the received signal is less than thedesired performance level, then the signal to interference ratiothreshold is increased. Conversely, if the performance level of thereceived signal is greater than the desired performance level, then thesignal to interference ratio threshold is decreased. It may seem counterintuitive to speak of a received signal being of too great a quality,but it should be remembered that this excess quality representsunnecessary energy employed in the transmission of forward link signals3, which results in degradation of service to all other mobile stationsserved by base station 1 and to a reduction in the number of mobilestations capable of being served by base station 1.

[0036] The varying of the signal to interference ratio thresholds basedon measured performance metrics is referred to as outer loop powercontrol. The feedback of power control commands based on comparing themeasured signal to interference ratio to the variable threshold isreferred to as closed loop power control. The combination of closed loopand outer loop power control is contemplated in both the ETSI UTRAcandidate submission and the TIA cdma2000 candidate submission. Thecombination of closed loop power control and open loop power control isdescribed in detail in aforementioned U.S. Pat. No. 5,056,109.

[0037] Mobile station 7 generates the power control commands andtransmits them along with traffic data, pilot symbol data back to basestation 1 on reverse link signals 5. In the exemplary embodiment,reverse link signals 5 are CDMA signals. In particular, in the exemplaryembodiment, reverse link signals 5 are CDMA signals transmitted inaccordance with the description in either the ETSI UTRA candidatesubmission or the TIA cdma2000 candidate submission. The reverse linksignals for these two submissions are essentially identical for thepurposes of the present invention. It should be understood that thepresent invention is equally applicable to other forms of CDMA signalsand to other modulation schemes such as TDMA or GSM modulation schemes.

[0038] Base station 1 receives the power control commands from mobilestation 7, and in response to those commands increases or decreases thetransmission energy of forward link signals 3. However, there may betimes when base station 1 does not respond to the power control commandsfrom mobile station 7. For example, base station 1 may not increase theenergy of forward link signals 3 in response to power control commandsfrom mobile station, when base station 1 determines that it cannotallocate additional energy for the transmission of forward link signals3 without causing unacceptable degradation to the transmission ofsignals to other mobile stations served by base station 1.

[0039] When base station 1 does not respond to the power controlcommands from mobile station 7, it can either continue transmitting atthe present transmission energy of forward link signals 3 (referred toherein in as “capping” the energy of forward link signals 3) or it cantemporarily gate off the transmission of forward link signals 3(referred to herein in as “gating” the energy of forward link signals3). When the energy of forward link signals 3 is either capped or gated,reception of those frames or symbols transmitted at the capped or gatedenergy in error is unreliable.

[0040] In response to the reception of the capped or gated frames orsymbols, mobile station 7 will erroneously increase its signal tointerference ratio threshold in the outer loop power control adjustmentdescribed above. This adjustment must be inhibited because the cause ofthe frame or symbols errors is not a result of mobile station 7 sendingincorrect power control commands but rather because base station 1 isignoring those commands and this is not within the control of mobilestation 7. The present invention addresses this problem of controllingadjustment of the outer loop power control system in the presence ofpotentially gated or capped signals.

[0041]FIG. 2 illustrates a simplified block diagram of base station 1.Information for transmission on forward link signals 3 is provided toencoder/interleaver 10, which provides forward error correction on thedata and then reorders the symbols in accordance with a predeterminedinterleaver format to provide time diversity in the transmitted signal.The interleaved encoded symbols are provided to modulator 12. In theexemplary embodiment, modulator 12 is a CDMA modulator, the design andimplementation of which is known in the art and is described in detailin the aforementioned U.S. Pat. Nos. 4,901,307 and 5,103,459. Inparticular, in the exemplary embodiment, modulator 12 is a CDMAmodulator capable of transmitting high speed data such as is describedin the aforementioned UTRA and cdma2000 specifications.

[0042] The modulated signal is provided to transmitter (TMTR) 14, whichup converts, amplifies and filters the signal for transmission. In theexemplary embodiment, transmitter 14 modulates the signals fortransmission using a quaternary phase shift keying (QPSK) modulationformat. The present invention is applicable to any form of modulation,such as BPSK, QAM or FSK modulation. The modulated signals are amplifiedto a level of transmission energy in accordance with a power controlsignal from power control processor 18. The QPSK signal is provided fromtransmitter 14 for transmission through antenna 16 as forward linksignals 3.

[0043] Turning to FIG. 3, the forward link signals 3 are received bymobile station 7 at antenna 50 and are provided through duplexer 52 toreceiver (RCVR) 54. Receiver 54 down converts, filters and amplifies thereceived signal and provides the received signal to demodulator 56. Inaddition, receiver 54 provides an indication of the in-band energy tosignal to interference ratio computation element 62 and to transmissiongating detector 68, the operation of which are described later herein.

[0044] Demodulator 56 demodulates the received signal and provides thedemodulated symbol data to de-interleaver/decoder 58.De-interleaver/decoder 58 reorders the demodulated symbols and decodesthe reordered symbols in accordance with a predetermined errorcorrection format such as a convolutional decoding or turbo decodingformat and provides the decoded data stream to the user of mobilestation 7 or for further processing prior to provision to the user ofmobile station 7. In addition, de-interleaver/decoder 58 provides asignal indicative of whether the frame was able to be reliably decodedor alternatively an indication of the symbol error rate in the decodedframe of data to threshold generator 70.

[0045] In the exemplary embodiment, information from receiver 54 andfrom demodulator 56 is provided to forward link power control processor60. Signal to interference ratio (SIR) computation element 62 estimatesthe signal to interference ratio of forward link signal 3.

[0046] A simplistic method of computing signal to interference ratiowould be to assume that all in-band energy is representative of theinterference energy. Because receiver 54 would typically include anautomatic gain control element that normalizes the signal based on theamount of in band energy, this value can be provided directly fromreceiver 54 to signal to interference ratio (SIR) computation element62. Demodulator 56 demodulates the received signal and extracts theforward link signal 3 from signals that are intended for transmission toother mobile stations served by base station 1. The energy of thedemodulated symbols are summed to provide a signal energy estimate. Thesignal energy estimate provided is then divided by the in band energyvalue to provide a rough estimate of the signal to interference ratio.

[0047] In the exemplary embodiment, forward link signal 3 is a variablerate transmission signal wherein the rate is unknown a priori to mobilestation 7. In the exemplary variable rate forward link signal 3, eachtransmitted signal is repeated within the transmission signal as manytimes as possible to fill a fixed length frame of data. More importantlyfor purposes of the present invention, the energy of the signal isvaried in inverse proportion to the amount of repetition in forward linksignal 3. This results in a constant symbol energy and approximatelyuniform performance across the rates.

[0048] This complicates the estimation of the signal energy because thesymbol energy is spread across time and, in order to determine thesufficiency of the symbol energy, the signal energy estimation algorithmmust have a fixed reference that does not vary with the unknown rate ofthe information. In the exemplary embodiment, power control bits arepunctured into forward link signal 3 and the energy of these bits is setat a fixed relation to the energy used in the transmission of themaximum rate information signal.

[0049] These non rate varying power control symbols can be used in oneof two ways. They can either be used to make a preliminary estimation ofthe rate of the information signal by estimating the ratio between thefixed energy power control symbols. The energy of the traffic data apreliminary estimate of the rate of the traffic data can be made andthis can be used to modify the computed traffic energy for comparisonwith a single non varying signal to interference ratio threshold.Alternatively, the preliminary rate estimation can be used such that thesignal to interference ratio is compared to a set of rate dependentthresholds.

[0050] An alternative method for using the power control bits that havea fixed transmission energy relationship to the transmission energy ofthe maximum rate information signal is to use the power control bitsthemselves to compute the signal energy. Under this method the energiesof the power control bits represent the signal energy and this energy iscomputed and used directly in the computation of the signal tointerference.

[0051] Another difficulty in computing the signal to interference ratioof the received CDMA signal is a result of the orthogonality of singlepath signals from base station 1 to mobile station 7. The problem isthat the in band energy does not accurately represent the interferenceenergy in a strong single path reception scenario such as when mobilestation 7 is in line of sight of base station 1. The in band energy willinclude energy that is orthogonal to forward link signals 3 and theorthogonal energy does not contribute to the interference limiting noisebecause it can be entirely eliminated in the demodulator.

[0052] In the exemplary embodiment, each base station modulates thesignal by first spreading the data in accordance with an orthogonalchannelization and then spreading the resultant orthogonally spread datain accordance with a pseudo noise (PN) sequence. PN sequences includeGold codes and maximal length codes the generation of which is wellknown in the art. One method of dealing with the additional complexityof orthogonal in band energy is to remove the PN spreading and tocompute the energy of the despread signal. This energy can then besubtracted from the in band energy to provide an estimate of theestimate of the noise signal. Another method is computing the varianceon a fixed energy signal that is part of forward link signal 3, such asa fixed energy pilot signal.

[0053] The complexities of computing the signal to interference ratio ina variable rate CDMA signal using orthogonal spreading is addressed inU.S. Pat. No. 5,903,554, filed Sep. 27, 1996, entitled “METHOD ANDAPPARATUS FOR MEASURING LINK QUALITY IN A SPREAD SPECTRUM COMMUNICATIONSYSTEM”, disclosure of which is assigned to the assignee of the presentinvention and incorporated by reference herein. It will be understood byone skilled in the art that the present invention is equally applicableto any method for computing the signal quality metric that is used tocompare against the threshold value.

[0054] Signal to interference ratio computational element 62 providesthe signal to interference ratio estimate to comparator 64. Incomparator 64 the signal to interference ratio estimate is comparedagainst the signal to interference ratio threshold. In the exemplaryembodiment, a single threshold is used and a single bit is provided fromcomparator 64 indicative of whether the signal to interference estimateis greater than or less than the signal to interference ratio threshold.This single power control bit is provided to power control bit generator(PC BIT GEN). PC bit generator 66 generates a power control command inaccordance with the comparison by comparator 64. The power controlcommand is provided to the transmission subsystem 77 of mobile station 7for transmission on reverse link signal 5.

[0055] As stated above, de-interleaver/decoder 58 provides a signalindicative of whether the frame was correctly decoded or whether a frameerasure was declared. Threshold generator 70 compiles a statistic of theframe error rate or other metric such as symbol error rate. In normaloperation, when the frame error rate rises above the desired frame errorrate threshold, generator 70 increases the signal to interferencethreshold and provides the new higher threshold value to comparator 64.Alternatively, in normal operation, when the frame error rate fallsbelow the desired frame error rate threshold, generator 70 lowers thesignal to interference threshold and provides the new lower thresholdvalue to comparator 64.

[0056] However, in the present invention, when forward link signal 3 isdetected to be capped or gated by transmission gating detector 68,transmission gating detector 68 sends a signal to threshold generator 70stopping its threshold updating operation and preventing any update ofthe frame error rate statistic of threshold generator 70.

[0057] In the exemplary embodiment, transmission gating detector 68detects gating of forward link signal 3 by computing the energy of thedemodulated signal from demodulator 56. If the energy is below apredetermined noise threshold, then forward link signal 3 is declared tobe gated off and the operation of threshold generator 70 is suspended.In the exemplary embodiment, transmission gating detector 68 detectssignal capping by recognizing an absence of increase in the energy offorward link signals 3 in response to a series of “up” commands beingsent back to base station 1. After a predetermined number of “up”commands have failed to increase the received energy of forward linksignals 3, forward link signal 3 is declared to be capped and theoperation of threshold generator 70 is suspended.

[0058] Returning to the operation of reverse link transmission subsystem77, information for transmission on reverse link signals 5 is providedto encoder/interleaver 78, which provides forward error correction onthe data and then reorders the symbols in accordance with apredetermined interleaver format to provide time diversity in thetransmitted signal. The interleaved encoded symbols are provided topower control puncturing element 76, which punctures the power controlsymbols into the outgoing data. The signal is then provided to modulator74. In the exemplary embodiment, modulator 74 is a CDMA modulator, thedesign and implementation of which is known in the art and is describedin detail in the aforementioned U.S. Pat. Nos. 4,901,307 and 5,103,459.In particular, in the exemplary embodiment, modulator 74 is a CDMAmodulator capable of transmitting high speed data such as is describedin the aforementioned UTRA and cdma2000 specifications and is describedin further detail in aforementioned copending U.S. patent applicationSer. No. 08/886,604.

[0059] The modulated signal is provided to transmitter (TMTR) 72, whichup converts, amplifies and filters the signal for transmission. In theexemplary embodiment, transmitter 72 modulates the signals fortransmission using a quaternary phase shift keying (QPSK) modulationformat. The present invention is applicable to any form of modulation,such as BPSK, QAM or FSK modulation. The QPSK signal is provided throughduplexer 52 for transmission through antenna 50 as reverse link signals5.

[0060] Returning to FIG. 2, reverse link signals 5 are received by basestation 1 at antenna 28 and are provided through to receiver (RCVR) 26.Receiver 26 down converts, filters and amplifies the received signal andprovides the received signal to demodulator 24. Demodulator 24demodulates the received signal and provides the demodulated symbol datato de-multiplexer 22. De-multiplexer 22 separates the power controlcommands from the signal and provides those commands to power controlprocessor 18.

[0061] The traffic data is provided to de-interleaver/decoder 20.De-interleaver/decoder 20 reorders the demodulated symbols and decodesthe reordered symbols data in accordance with a predetermined errorcorrection format such as a convolutional decoding or turbo decodingformat and outputs the decoded data stream to a base station controller(not shown).

[0062] Under normal operation, power control processor 18 generates anew transmission power for the transmission of forward link signals 3 inaccordance with the received power control commands. However, powercontrol command processor 18 also determines the transmission energy offorward link signals 3 in accordance with transmission control data. Thetransmission control data will for example provide a maximumtransmission energy for the transmission of forward link signals 3. Whenin response to the received power control commands, the transmissionenergy would exceed the allowed maximum transmission of the forward linksignals 3, then the transmission energy of forward link signals 3 iseither gated or capped and the operation proceeds as described above.

[0063]FIG. 7 illustrates the operation of the base station in a cappedand gated operation. Curve 250 illustrates the path quality between thebase station and the mobile station. Curve 252 illustrates thetransmission power in response to changes in the path quality. Thetransmission energy should inversely track the path quality or in otherwords the transmission energy should track the path loss. When the pathloss is increased by an amount Δ, the transmission power should beincreased by Δ. The horizontal line 256 represents the maximum transmitpower of the base station. At this point, there is no remainingtransmission power available.

[0064] In frame one, the desired transmission energy is always less thanthe maximum supply power. So in frame one the transmission energy cantrack the path loss. In frame 2 the path loss has increased to an extentthat at point 260, the transmission energy can no longer track the pathloss. At this point, in the exemplary embodiment, the transmissionenergy is capped which is represented by the flattening of the suppliedtransmission power and the separation between the actual suppliedtransmission power and the desired supplied transmission power.

[0065] It should be noted that it is the transmission energy of thededicated forward link signals 3 that is capped. In an alternativeembodiment, the portion of frame 2 following point 260 could be gated.In a second alternative embodiment, the transmission energy at the pointbeyond point 260 could depend on the point within the frame that therequested energy passed the threshold 256. For example, if the requestedenergy passed threshold 256 more than half way through the transmissionof frame 2 then the energy would be capped. If the requested energypassed threshold 256 less than half way through the transmission offrame 2 then the energy would be gated.

[0066] In the exemplary embodiment, the dedicated forward link signalsinclude the traffic channel signals and the power control commands.While the traffic channel signals are capped or gated, the power controlcommands are still transmitted by the base station at the desired supplypower. That is to say, even beyond point 260, the reverse link powercontrol commands transmitted by the base station are still tracking thedesired supply power curve 254 or a curve of a fixed relation to thedesired power curve 254. This means that the mobile station is capableof sending power control commands that track the path loss even when thetransmission power of the traffic channel data is capped or gated.

[0067] Although base station 1 does not transmit the traffic data at thedesired supply power, it still tracks the changes requested by themobile station. In this fashion, base station 1 is capable ofdetermining at point 262 where the desired supply power is less than themaximum supply power. In the exemplary embodiment, the fourth frame isgated in its entirety and the subsequent frame is transmitted at thedesired supply power indicated by curve 258.

[0068] II. Outer Loop Control Based on Decoder Metrics and AccumulatedFrame Energy

[0069] In this second embodiment of the present invention the outer loopis controlled by factors in addition to the frame error rate. In a firstaspect of the second embodiment, before changing the outer thresholdbased on a frame error or a correctly received frame, the receiverdetermines whether the frame was received with accumulated energy overthe frame in excess of the outer loop threshold.

[0070] If the frame was received correctly, the conventional responsewould be to incrementally reduce the SIR threshold. However, if theframe was received correctly but the accumulated energy over the framewas in excess of the threshold, then it is inappropriate to reduce theenergy threshold. Conversely, if a frame is received in error, theconventional response would be to incrementally increase the SIRthreshold. However, if the frame was received in error and theaccumulated energy over the frame was less than the threshold SIR, thenit is also inappropriate to increase the SIR threshold. Both of theseresponses are inhibited in the second embodiment of the presentinvention.

[0071] Moreover, the present invention will also provide a method forimproving the amount of change in the outer loop SIR threshold. Forexample, if the frame was received correctly and the accumulated energyover the frame was below the threshold in excess of a predeterminedamount, then the threshold should be lowered by an amount greater thanthe amount that the threshold should be lowered should the frame havebeen received correctly and the frame energy is at the threshold amount.Conversely, if the frame was received in error and the accumulatedenergy over the frame was in excess of the threshold more than apredetermined amount, then the threshold should be increased by anamount greater than the amount that the threshold should be increasedhad the frame been received in error with an accumulated energy at thethreshold amount.

[0072] Furthermore, the present invention will also provide a method forimproving the amount of change in the outer loop SIR threshold incontradiction to the frame error rate when decoder metrics indicate thatsuch a change is required. For example, if the frame was receivedcorrectly but the decoder metrics indicate that the decoder is veryclose to failing then either the adjustment of the outer loop will befrozen or the threshold will be increased.

[0073]FIG. 4 is a flow diagram of operation of power control in themobile station. At step 100 the mobile station receives the signal. Atdecision diamond 102, the mobile station determines if the signal isgated or chopped, i.e. capped. If the signal is not gated and is notchopped, the mobile station computes the SIR of the received signal atstep 106 and compares the SIR with an outer loop threshold at step 108.The mobile station then generates a PC command at step 110. Returning todecision diamond 102, if the received signal is not gated or chopped,the processing continues to step 104 to freeze further outer loopcalculations, i.e., stop adjusting SIR threshold. If the outer loop isfrozen at decision diamond 112, the process stops. If the outer loop isnot frozen at decision diamond 112, i.e. the mobile station is stilladjusting SIR thresholds, processing continues to step 114 to adjust theouter loop if necessary.

[0074]FIG. 5 is a flowchart implementing a simplified version of thepresent embodiment. The method used to determine changes in the SIRthreshold will be described in conjunction with the receiver structureillustrated in FIG. 3. In block 200, de-interleaver/decoder 58 sends anindication to threshold generator 70 as to whether the frame wasreceived correctly.

[0075] If the frame was received correctly, the process moves to block202. Indication of the received energy is provided from receiver 54 tothreshold generator 70. If the frame was received with an accumulatedenergy greater than an accumulated frame energy threshold, the SIRthreshold is frozen. The reason for this is that the correct receptionof the frame does not reflect the accuracy of the threshold, since theenergy of the received frame was in excess of that threshold. This canhappen, for example, if the propagation path rapidly improves and thedown commands from mobile station are inadequate to reduce the excessenergy of the transmitted signal.

[0076] If the frame was not received with excess energy then the processmoves to decision block 206. De-interleaver/decoder 58 sends anindication of the decoder metrics to threshold generator 70. The decodermetrics are an indication of how close the decoder is to failing to beable to decode the frame. Decoder metrics that are applicable includeaccumulated metrics in a trellis decoder, number of corrected symbolerrors or the number of iterations required for successful decoding. Ifthe decoder metrics are good indicating that the decoder is operatingnear its optimal decoding strength, then the threshold is increased inblock 208. If the decoder metrics are bad indicating that the decoder isoperating near its breaking point at which it will be unable tosuccessfully decode the frame, then the threshold is increased in block210.

[0077] Back in block 200, if the frame was received in error, then theprocess moves to block 212. Indications of the received energy areprovided from receiver 54 to threshold generator 70. If the frame energywas in excess of the accumulated received frame energy threshold, thenthe process moves to block 214 and the SIR threshold is increased. Ifthe received energy was less than the accumulated frame energythreshold, then the process moves to block 216 and the threshold isfrozen.

[0078]FIG. 6 illustrates a preferred embodiment wherein the adjustmentsto threshold are based on the frame error rate, the received SIR of theframe and the decoder metrics, and in particular vary based on thereceived SIR. Points on the vertical axis represent the amount ofadjustment to the threshold. Points below the horizontal axis representdecreases to the SIR threshold and points above the horizontal axisrepresent increases to the SIR threshold. Points on the horizontal axisrepresent the received SIR of the frame minus SIR threshold previouslyused. Points to the left of the vertical axis represent received frameSIR values less than the current SIR threshold and points to the rightof the vertical axis represent received frame SIR values greater thatthe current SIR threshold.

[0079] There are four curves represented on the graph of FIG. 6. Fromwhich curve one extracts the amount of change to the SIR thresholddepends on whether the frame was received in error and on the decodermetrics. If the frame was received in error the amount of change to theSIR threshold is selected from curve 250. If the frame was receivedcorrectly and the decoder metrics indicate that the decoder is operatingnear optimum decoding power, then the change to the SIR threshold isselected from curve 254. If the frame was received correctly and thedecoder metrics indicate that the decoder is operating with very littlemargin, then the change to the SIR threshold is selected from curve 252.If the frame was received correctly and the decoder metrics indicatethat the decoder is operating with more margin than desired, then thechange to the SIR threshold is selected from curve 256.

[0080] At point 258 on curve 250, the frame was received in error andthe received SIR was greater than the threshold by a significant amount.Thus, the change to the threshold is greater than the change to thethreshold had the frame been received in error with the received SIR atthe threshold value illustrated by point 260. At point 262, the frame isreceived correctly with nearly optimal decoder metrics and the receivedSIR is less than the threshold by a significant amount. Thus, thedecrease in the SIR threshold is more than the decrease had the framebeen received correctly with nearly optimal decoder metrics and thereceived SIR is at the threshold illustrated by point 264.

[0081] The previous description of the preferred embodiments is providedto enable any person skilled in the art to make or use the presentinvention. The various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the use ofthe inventive faculty. Thus, the present invention is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

I (WE) CLAIM:
 1. An apparatus for controlling the transmission energy ofsignals received from a remote transmitter, comprising: receiver formeasuring an energy of the signals to produce an energy indication; andpower control processor for generating a signal quality metric based onsaid measuring, generating closed loop power control commands inaccordance with a comparison between the signal quality metric and avariable threshold, making a determination that the remote transmitteris not responding to the power control commands in a predeterminedfashion, and suspending an updating of the variable threshold inaccordance with said determination.
 2. The apparatus of claim 1 whereinsaid signal quality metric is a signal to interference ratio, andwherein said power control processor comprises a signal to interferenceratio computation element for generating said signal to interferenceratio based on the energy indication.
 3. The apparatus of claim 1further comprising a demodulator for demodulating the signals andmeasuring demodulated symbol energies from symbols residing in saidsignals, and providing said demodulated symbol energies to said powercontrol processor, wherein said power control processor generates saidsignal quality metric based on said demodulated symbol energies.
 4. Theapparatus of claim 1 further comprising a decoder for decoding framesresiding in said signals and generating frame error information, andproviding said frame error information to said power control processor,and wherein said power control processor makes said determination basedon said frame error information.
 5. The apparatus of claim 1 furthercomprising a decoder for decoding frames residing in said signals andgenerating a decoder metric, and providing said decoder metric to saidpower control processor, and wherein said power control processor makessaid determination based on said decoder metric.
 6. The apparatus ofclaim 1 further comprising a decoder for decoding frames residing insaid signals and generating a decoder metric and frame errorinformation, and providing said decoder metric and frame errorinformation to said power control processor, and wherein said powercontrol processor makes said determination based on said decoder metricand frame error information.
 7. A method of controlling a transmissionenergy of signals received from a remote transmitter, comprising:measuring an energy of the signals to produce an energy indication;generating a signal quality metric based on said measuring; generatingclosed loop power control commands in accordance with a comparisonbetween the signal quality metric and a variable threshold; making adetermination that the remote transmitter is not responding to the powercontrol commands in a predetermined fashion; and suspending an updatingof the variable threshold in accordance with said determination.
 8. Themethod of claim 7 wherein said signal quality metric is a signal tointerference ratio.
 9. The method of claim 7 further comprisingdemodulating symbols residing in the signals to produce symbol energies,wherein said generating said signal quality metric is based on saiddemodulated symbol energies.
 10. The method of claim 7 furthercomprising decoding frames residing in the signals to produce frameerror information, wherein said making a determination is based on saidframe error information.
 11. The method of claim 7 further comprisingdecoding frames residing in the signals to produce a decoder metric,wherein said making a determination is based on said decoder metric. 12.The method of claim 7 further comprising decoding frames residing in thesignals to produce a decoder metric and frame error information, whereinsaid making a determination is based on said decoder metric and frameerror information.
 13. The method of claim 7 wherein said making adetermination comprises detecting a gating of the transmission energy ofthe signals based on said energy indication.
 14. The method of claim 7wherein said making a determination comprises recognizing an absence ofincrease in said energy indication in response to at least one of saidclosed loop power control commands.